1. Field of the Invention
The present invention relates to the field of semiconductor processing and more specifically to a surface treatment of a silicon dioxide film on a semiconductor wafer substrate and methods and devices utilizing this surface treatment, particularly as applied in a single wafer tool.
2. Discussion of Related Art
In semiconductor manufacturing, the qualities of the gate insulator in a transistor are important in determining the capacitance of the transistor. An important quality of the gate insulator in determining the capacitance is the dielectric constant (relative permittivity.) In gate insulators it is desirable to have the highest capacitance possible. For this, the gate insulator must have a high dielectric constant. The direct relationship between the capacitance and the dielectric constant of the insulator is demonstrated by the following equation for capacitance. In this equation Cox is the capacitance value of two electrodes with an insulator in between:       C    ox    =                    ϵ        t            ⁢              ϵ        o            ⁢      A              t      ox      
In this equation ∈r is the dielectric constant of the insulator, ∈o is the dielectric constant of vacuum, A is the area of the capacitor, and tox is the thickness of the insulator. Hence, the variables that may be manipulated to affect the capacitance are the dielectric constant of the insulator, the area of the capacitor, and the thickness of the insulator.
In the current state of the art, silicon dioxide is used as the gate insulator in transistors. Silicon dioxide has a dielectric constant of approximately 4.0. As devices are downscaled both the area (A) of the capacitor and the thickness (tox) of the insulator are decreased. The effect this downscaling has on the capacitance can be explained by the above equation. As the area is decreased the capacitance value will decrease. But, as the thickness is also decreased the capacitance value will increase. Therefore, as devices are downscaled, silicon dioxide may continue to be used as the gate insulator as long as its thickness is decreased along with the decrease of the capacitor""s area.
The industry is now using the minimum thickness and the minimum area for gate insulators. Because these values are now constant, the only variable left that may be manipulated to increase the capacitance, while still decreasing the area (A), is the dielectric constant of the gate insulator. The capacitance of the transistor may be increased by increasing the dielectric constant of the gate insulator. Insulating materials with higher dielectric constants than silicon dioxide (higher than 4.0) must be used. Examples of such high dielectric constant materials are silicon oxynitride, silicon nitride (Si3N4), Ta2O3, and PZT (PbZrTiO3).
But the use of such insulators poses a significant problem. These materials cannot be applied directly to a silicon substrate. In semiconductor processing, a silicon substrate is monocrystalline silicon that serves as the lowest layer of a wafer. A layer of silicon dioxide (native oxide) must exist between the insulating material and the silicon substrate. This layer of silicon dioxide will lower the overall dielectric constant of the gate insulator. Therefore, the dielectric constant of the silicon dioxide film must be increased in order to minimize the effect it has on lowering the overall dielectric constant of the film.
Thus, what are desired are a method and a device in which the overall dielectric constant of the gate insulator is maximized. To do this the silicon dioxide film that is sandwiched in between the silicon substrate and the high dielectric constant insulating material layer must have the highest dielectric constant possible. The present invention provides a method and device wherein the overall dielectric constant of the gate insulator is maximized.
The present invention shows a method and a device utilizing a novel surface termination of a silicon dioxide film for use in a single wafer cleaning tool. According to the present invention, the surface termination used in both the methods and the devices is ammonium oxide (xe2x80x94Oxe2x80x94NH4). In the present invention a silicon dioxide film is first formed on a silicon substrate, and that silicon dioxide film is then terminated with xe2x80x94Oxe2x80x94NH4. In one embodiment, this termination is accomplished by dispensing a mixture containing ammonium ions onto the silicon dioxide film. Further embodiments describe methods of accomplishing the termination through the use of a single wafer cleaning tool to prevent the etching of the film by the mixture containing ammonium ions. Other embodiments describe an insulator device and a wafer device.